Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$80.78	13.302%	$91.5254	$91.53	$91.55	$91.50
Purchase #2	$115.27	9.574%	$126.3059	$126.31	$126.30	$126.30
Purchase #3	$96.88	12.750%	$109.2322	$109.23	$109.25	$109.20
Purchase #4	$41.87	13.754%	$47.6288	$47.63	$47.65	$47.60
Purchase #5	$82.60	3.556%	$85.5373	$85.54	$85.55	$85.50
Purchase #6	$17.87	13.412%	$20.2667	$20.27	$20.25	$20.30
Purchase #7	$50.77	8.149%	$54.9072	$54.91	$54.90	$54.90
7 purchase totals =	$486.04		$535.4035	$535.42	$535.45	$535.30